This invention relates to shock absorbers. In particular, this invention relates to an improved structure for an adjustable shock absorber that includes one or more microvalves to control fluid flow in a valve assembly arranged between working chambers in a shock absorber pressure tube and/or in a shock absorber reservoir.
Shock absorbers are used in connection with automotive suspension systems to dampen vibrations, control rate of weight transfer, and improve vehicle comfort and performance. To perform these functions, shock absorbers are generally connected between the body and the suspension of the motor vehicle.
Common shock absorbers for automobiles may be either a mono-tube design or a dual-tube design. In the mono-tube design, a piston is located within a pressure tube and is connected to the sprung mass of the vehicle through a piston rod. The pressure tube is connected to the unsprung mass of the vehicle. The piston divides the pressure tube into an upper working chamber and a lower working chamber. A conventional piston includes compression valves, which limit the flow of damping fluid from the lower working chamber to the upper working chamber during a compression stroke, and rebound valves, which limit the flow of damping fluid from the upper working chamber to the lower working chamber during a rebound or extension stroke. Because the compression valves and the rebound valves have the ability to limit the flow of damping fluid, the shock absorber is able to produce a damping force which counteracts the vibrations and weight transfer which would otherwise be transmitted from the unsprung mass to the sprung mass.
In a dual-tube shock absorber, a fluid reservoir is defined between the pressure tube and a reservoir tube which is positioned around the pressure tube. In both a mono-tube and a dual-tube shock absorber, a base valve assembly may be located between the lower working chamber and a fluid reservoir to control the flow of damping fluid. In such a shock absorber, compression valves are located in the base valve assembly. In addition to the compression valves, the base valve assembly will include a check valve assembly which allows unrestricted fluid flow in one direction into the lower chamber from the reservoir during a rebound stroke. The compression valves of the base valve assembly and the compression valves of the piston assembly together produce the damping force during a compression stroke, and the rebound valves of the piston produces the damping force during a rebound or extension stroke.
The valve assemblies in the shock absorber control fluid flow between the two chambers and the reservoir during the stroking of the shock absorber. By controlling the fluid flow between the two chambers and the reservoir, pressure drops and pressure increases occur, and contribute to the damping forces of the shock absorber. The valve assemblies can be used to tune the damping forces to control ride and handling as well as noise, vibration, and harshness.
Shock absorbers may be adjustable to meet driver preferences. For example, a driver may prefer a softer performance or feel on rough roads and a firmer feel on smooth roads. Generally, the greater degree to which the flow of damping fluid within the lower working chamber is restricted, the greater are the damping forces provided by the shock absorber. Thus, a soft compression and rebound stroke is produced when the flow of damping fluid is relatively unrestricted and a firm compression and rebound stroke is produced when the flow of damping fluid is restricted.
However, a conventional base valve assembly is not adjustable between desired soft, medium, and firm performance settings. Thus, it would be desirable to provide an improved structure for a valve assembly arranged between working chambers in a shock absorber pressure tube and/or in a shock absorber reservoir.